1. Field of the Invention
The present invention relates to cephem derivatives having antibacterial activity effective against a wide spectrum of bacteria. More particularly, the present invention relates to novel cephem derivatives having substituted or unsubstituted imidazo[5,1-b]-thiazolium-6-yl as a substituent at the 3-position of the cephem ring.
2. Background Art
Cephem antibiotics exhibit excellent antibacterial activity with a low toxic for mammals. They are therefore remarkably effective in the treatment of infectious diseases in mammals. Those cephem derivatives which have an aminothiazolylacetyl group at the 7-position of the cephem ring have potent antibacterial activity and stability agaist beta-lactamase. For this reason, numerous studies and developments in these cephem derivatives have been made in recent years.
Onium-salt-type cephem antibiotics, such as ceftazidime and cefpirome, which have an aminothiazolylacetyl group at the 7-position and a quaternary salt substituent at the 3-position have potent antibacterial activity effective against a wide spectrum of bacteria from Gram-positive bacteria to Pseudomonas aeruginosa. Thus, numerous studies and developments in the antibiotics of this type have been made in many countries in the world. However, even the onium-salt-type cephem compounds such as ceftazidime and cefpirome may not be satisfactory in the antibacterial activity against Pseudomonas aeruginosa or Gram-positive bacteria such as Staphylococcus aureus which have brought about a clinical problem in recent years. In addition, infectious diseases caused by methicillin-resistant Staphylococcus aureus (MRSA) or penicillin-resistant streptococcus pneumoniae (PRSP) have been a serious clinical problem these days. It is therefore strongly demanded to obtain novel cephem antibiotics which have improved antibacterial activity also against these bacteria (Chapter 11 by W. E. Wick, "Cephalosporins and Penicillins, Chemistry and Biology" edited by E. H. Flynn, Academic Press, New York, N.Y., 1972; 18.1 "Cephalosporins" by Hatsuo Aoki, "The Leading Studies in Antibiotics" edited by Masaji Oho and Satoshi Omura, Tokyo Kagaku Dojin Kabushiki Kaisha, Japan, 1987; and "Manifestation of Resistance and Molecular Genetics" by Ryoichi Okamoto and Matsuhisa Inoue, "Sogo Rinsho", Vol. 42, No. 2, 1993).